Such a hydraulic steering unit is known, for example, from U.S. Pat. No. 4,676,334.
The variable first and second orifices are arranged in a kind of Wheatstone bridge, in which one diagonal of the bridge arrangement is connected to the pressure port and to the tank port and the other diagonal of the bridge arrangement is connected to the two working ports.
When a steering motor connected to the working port arrangement should be steered to the left, for example, the variable first left orifice is opened and at the same time the variable second right orifice is opened so that the flow of hydraulic fluid is directed through the left working flow path to the steering motor and from the steering motor back through the right working flow path and the second right orifice to the tank.